Consumers of electrical power today are often charged by electrical utilities for both total power consumption during a billing period as well as for peak demand. This charge for peak demand is made irrespective of actual consumption made by the consumer during any specific period. The justification for this charge rests in the necessity of the utility having to have the resources available to provide power during peak demand periods. In other words, it compensates the utility company for having to have the capacity available to service their customers during brief peak demand periods which capacity may remain idle during the remaining periods of each day and month.
Though billing periods of power companies normally cover a substantially long period of time such as a month, peak demand is calculated on a relatively short period of time such as a quarter or half hour basis. Accordingly, utility companies meter both the total power supplied to their customers during each billing period as well as the maximum power delivered during any brief period in a succession of periods that cumulatively form the billing period. The maximum demand recorded during any of these brief periods in any one month is then imputed into a billing formula, exemplary of which is: ##EQU1## WHERE T.sub.2 is the aforementioned relative brief period of time such as a quarter hour or half hour and T.sub.1 is the relative long billing period such as a month.
Typically, the electrical load that imposes the greatest demand for electricity for the majority of utility company customers is their temperature control systems, be it an air conditioning or electrical heating unit. Thus, on hot summer days, air conditioners usually account for peak demand of customers whereas in winter their heaters account for peak demand. These temperature control units are themselves ordinarily controlled by thermostats which cyclically couple the system with line voltage dependent upon sensed temperatures at which they are set to respond. Their control function therefore is eventually divorced from the just described method or formula by which their consumption cost is calculated.
Accordingly, it is the general object of the present invention to provide means for limiting peak power demand.
More specifically, it is an object of the present invention to provide an electrical circuit for limiting peak power demand of air temperature control systems such as air conditioning and electrical heating systems.
Another object of the invention is to provide a power demand limiting circuit of the type described which is easily incorporated into preconstructed circuits supplying power to air temperature control systems.
Yet another object of the invention is to provide a power demand limiting circuit of the type described which may be selectively activated and deactivated with facility.